There is illustrated herein in embodiments, an architecture including methods and systems for synchronizing between elements in a distributed system. For example, a distributed system may include a collection of modules, each with its own function. The collection of modules may be interconnected to carry out a particular function or functions. The interconnection may be physical and/or logical in nature. Modules may be connected by a network or other communications scheme. Communications media may include wire, coaxial cable, fiber optics and/or radio frequency (RF) transmissions. The network or communications scheme may be associated with communication delays. Synchronizing controllers or processes in the face of such delays can be problematic. Some document processors are implemented as distributed systems and embodiments will be described with reference thereto. However, embodiments of the methods and systems described herein may be beneficially applied in a wide variety of control system environments.
Document processors include, for example, printers, copiers, facsimile machines, finishers and devices for creating documents, such as word processors and desk top publishers. In some instances, document processors provide the services of two or more of these devices. For instance, document processors that provide printing, copying, scanning, and faxing services are available. Printers and copiers can include feeders that supply print media and finishers that staple, shrink wrap or otherwise bind system output. Finishers may also fold or collate documents.
In order to increase throughput, some printers and copiers are being developed which include two or more marking engines. For example, U.S. patent application Ser. No. 10/924,113 filed Aug. 23, 2004 by Jonas M. M. dejong, et al. for a Printing System with Inverter Disposed for Media Velocity Buffering and Registration; U.S. patent application Ser. No. 10/924,106 filed Aug. 23, 2004 by Robert M. Lofthus, et al. for a Printing System with Horizontal Highway and Single Pass Duplex; U.S. patent application Ser. No. 10/924,459 filed Aug. 23, 2004 by Barry P. Mandel, et al. for a Parallel Printing Architecture Consisting of Containerized Image Marking Engine Modules; U.S. patent application Ser. No. 10/860,195 filed Jun. 6, 2004 by Robert M. Lofthus, et al. for a Universal Flexible Plural Printer to Plural Finisher Sheet Integration System; U.S. patent application Ser. No. 10/881,619 filed Jun. 30, 2004 by Daniel G. Bobrow for a Flexible Paper Path Using Multidirectional Path Modules; U.S. patent application Ser. No. 10/761,522 filed Jan. 21, 2004 by Barry P. Mandel, et al. for a High Print Rate Merging and Finishing System for Parallel Printing; U.S. patent application Ser. No. 10/785,211 filed Feb. 24, 2004 by Robert M. Lofthus, et al. for a Universal Flexible Plural Printer to Plural Finisher Sheet Integration System; and U.S. patent application Ser. No. 10/917,768 filed Aug. 13, 2004 by Robert M. Lofthus for a Parallel Printing Architecture Consisting of Containerized Image Marking Engines and Media Feeder Modules, all of which are incorporated herein by reference, describe aspects of tightly integrated document processing systems including a plurality of marking engines.
Additionally, some printers and copiers are being developed using a hypermodular structure to increase modularity and flexibility. These systems may possess a number of distributed processors, sensors, and actuators. For example, U.S. patent application Ser. No. 10/357,687 filed Feb. 4, 2003 by David K. Biegelsen, et al., for Media Path Modules; U.S. patent application Ser. No. 10/357,761 filed Feb. 4, 2003 by Markus P. J. Fromherz, et al., for Frameless Media Path Modules; U.S. patent application Ser. No. 10/740,705 filed Dec. 19, 2003 by David K. Biegelsen, et al., for a Flexible Director Paper Path Module; and U.S. patent application Ser. No. 10/812,376 filed Mar. 29, 2004 by David G. Duff, et al., for a Rotational Jam Clearance Apparatus, all of which are incorporated herein by reference, describe aspects of tightly integrated document processing systems including hypermodules.
Some systems, including some document processing systems, are based on a centralized control architecture wherein a single computational platform controls all system actuators and receives all system feedback information. These architectures work well where the systems are relatively small and are of a fixed or unchanging configuration. However, as system size increases, the computational capabilities of a single platform can be overwhelmed. Additionally, providing individual interfaces between the single computational platform and each of the sensors and actuators of the system can be impractical. Furthermore, where it is desirable to assemble or reconfigure a system from various subcomponents, the direct interfacing of sensors and actuators to the central platform becomes problematic.
These factors have led to the development of systems based on network communications. For example, U.S. Pat. No. 6,615,091 B1 to Birchenough, et al. for a Control System and Method Therefore allegedly disclosed an embodiment of a distributed control system including a main control coordinator, three local process station controllers and a designated number of process module controllers, each associated with a process module. The control system allegedly provides a real time operating system and has a communication bus platform provided via an Ethernet™ communication bus and a second bus to connect the controllers in a distributed control network. The Ethernet™ bus connects the main control coordinator and each of the local process station controllers and a continuous motion conveyer controller. Each of the process module controllers are connected via the second bus to designated local process station controllers.
In the system of Birchenough, the main controller agent interacts with each of the process station agents, and each of the process station agents interacts with each of the process module agents that are assigned thereto. During normal manufacturing operation, the main controller coordinator agent sends article notice messages to the process station agents to notify the process station agents of the oncoming articles of manufacture. A process station normally will not process the article of manufacture unless the process station agent which controls a particular process module has received an article notice message indicating that it should do so and the continuous feed indexer has returned a report that it is in proper position. In response, the process station agent notifies the designated process module agent to initiate its programmed process operation. Once the process module has completed its intended operation, the process module agent issues a work report message which is sent to the process station agent. The process station agent then broadcasts the work report message to other process stations as well as to the main control coordinator.
It appears that in the system of Birchenough, et al., a single entity (e.g., the main coordinator) is aware of and maintains information regarding each task, object or workpiece being processed by the system, and is thereby able to issue commands orchestrating the activities of system components. However, this may limit the scalability of the system. For example, as the size of the system increases, the capabilities and/or resources of the main control coordinator (or processor running the main control coordinator) may be overwhelmed. Therefore, it may be desirable to distribute some of this functionality over a number of processors or controllers.
However, as machines become more complex and contain larger numbers of embedded processors, instances of tightly coupled distributed control systems are becoming more common. In a tightly coupled system, controllers may interact through fast physical or informational coupling. That is, the actions of one controller may have an impact on an ability of a second controller to perform its function. Therefore, there is a desire for coordination and communication among the various controllers. One aspect of the coordination problem is how to synchronize a newly activated process or controller, which has been activated in order to address a particular portion of a process, to the status or state of the ongoing process in the face of communication delays.
United States Patent Application Publication No. U.S. 2002/0194269 A1, published Dec. 9, 2002 by Owada, et al. entitled “Distributed Process System, Distributed Processing Method and Client Terminal Capable of Using the Method,” allegedly discloses a distributed processing system wherein a user terminal receives event information generated in other user terminals and transferred from a server. During a period that the event information is transmitted in a network, a model in a processing server becomes different from a model in the user terminal. Then, a state change compensation portion continuously changes a state model processed in a processing portion so that it becomes the same as the state of the model in the processing server, whereby an influence of delay generated by a communication can allegedly be reduced. The application appears to be directed toward compensating for network delays in a multi-player video game environment.
United States Patent Application Publication No. U.S. 2002/0178292 A1, published Nov. 28, 2002 by Mushkin, et al., entitled “Distributed Synchronization Mechanism for Shared Communications Media Based Networks,” allegedly discloses a distributed synchronization mechanism in which a synchronization loop of each station on a shared media based network considers only synchronization signals received having a time phase earlier than the time phase of its internal clock. Therefore, the station with the fastest internal clock effectively functions as an ad hoc synchronization master for all stations in a given connected group.
However, the phase selecting technique of Mushkin is not applicable to the more complex synchronizations required in and between control processes. The video game synchronizing of Owanda is temporary in that synchronization is not necessarily maintained after an initial synchronization event.
Therefore, there is a desire for systems and methods for synchronizing a second process to a first process in the face of communications delays.